Synthetic polymers such as acrylic polymers have, for the most part, replaced naturally occurring materials such as animal glues, starches and vegetable gums in many adhesive applications. The key to this replacement was the development and use of tackifier resins in the formulation with synthetic polymers, because they give the system the ability to wet the substrate surface and thus form a strong bond. Without tackifiers in the adhesive formulation, the synthetic polymers have low tack and peel adhesive performance.
Various resinous materials have been suggested as tackifiers for synthetic polymers. Examples of materials suggested include rosin, disproportionated rosin, rosin esters such as glycerol esters of rosin and pentaerythritol esters of rosin, aliphatic hydrocarbon resins from petroleum, aromatic petroleum resins, DCPD (dicyclopentadiene) resins, terpene resins, terpene/phenol resins and cumarone/indene resins.
Tackifiers are resins that can be considered as high viscosity solvents for the base polymer. The term tackifier therefore, cannot be given to any material unless we relate that material to the product that it tackifies.
Acrylic polymer compositions have long been used as adhesive compositions, particularly in PSA (pressure sensitive adhesive) compositions. Common PSA compositions include a high-molecular-weight acrylic base polymer and a tackifying resin and when required, plasticizer, stabiliser, antioxidant, filler, colouring agent and the like. PSA compositions should have a high initial tack so that the adhesive surface merely needs to be contacted and pressed to the surface to achieve bonding. There should be little or no requirement to hold the adhesive and substrate in position for any significant time while a bond develops.
In developing adhesive formulations one seeks the optimum combination of several adhesive properties and since it is not generally possible to achieve the optimum for every property it is necessary to obtain the best balance of properties for the particular use in mind. In e.g. PSA compositions that are used in the label industry one tries to optimise the loop tack and peel and at the same time provide an adhesive whose component will not migrate during storage.
Nowadays mainly rosin derivatives, such as disproportionated rosin acids, and hydrocarbon resins are commercially used as tackifiers for adhesive compositions comprising acrylic polymers. The rosin derivatives have been preferred due to better compatibility with acrylics.
Initially most important were the solvent acrylics, but environmental, health and safety needs of industry have resulted in dramatic growth in water borne adhesive compositions comprising acrylic polymers. With increasing desirability of water borne systems and often their demonstration of significant performance enhancements with tackifier resins, new tackifier resins suitable for these systems are being sought.
EP 300624 discloses acid functional polymer resins which are obtained by polymerising an olefin or mixture of olefin, reacting the formed polymer with an acid to form an acid functional polymer which polymer subsequently is neutralised with a base.
The present resin composition combines the good adhesive properties of rosin among other no bleed trough, with the short reaction times generally applied for the synthesis of hydrocarbon resins. Another advantage with the present resin composition is that it provides improved adhesion properties of PSA compositions on non-polar surfaces. In addition, this resin composition has an improved smell and colour over the traditional hydrocarbon resins made by thermal polymerisation, without the need of a hydrogenation step. A further advantage with the present invention is to provide a resin composition comprising a minimum amount of rosin derived from natural sources thereby reducing the cost of production.